WASHINGTON
— Cutting government spending wasn't something George W. Bush talked about much during the election campaign. But as he unveils his budget this week - and continues hawking his big tax cut - he's suddenly promoting a dramatic new doctrine of fiscal belt-tightening. Yet his approach is unlike anything in recent Washington memory. It's not nearly as hard-line as Ronald Reagan's "get government off the backs of the people" pitch - or Newt Gingrich's anti-school-lunch creed. In fact, President Bush actually wants to boost spending on things like education, medical research, and the military.

Indeed, Mr. Bush's new orthodoxy represents a third-way Republicanism that's all about lean-yet-active, efficient-yet-engaged government. But many wonder whether he can pull it off.

To spend more on some things - without spending more on the total - may be a feat for Hercules, or perhaps a Zen master. Furthermore, Bush will also have to buck two big realities: Washington's tradition of ever-expanding budgets - and new temptations to spend the federal surplus.

For all of his plans to shrink government, President Reagan cut overall spending in just one year out of his eight in power. (In the past 60 years, total government spending has shrunk just 10 times.)

It's clear Bush will have to beat back a bipartisan penchant for spending - and risk angering Democrats and Republicans alike. He'll have to rely on fiscal conservatives from both parties to keep the budget at what he calls "responsible" levels.

Bush has already started steeling himself for attacks from both sides. "This is a town," he said in a news conference Friday, "where if you don't increase the budget by an expected number, it's considered a cut." But, he said pointedly, "In my parlance, it's not a cut." And he promised to slow the growth in spending.

But that's hard to do. Entitlements - such as Medicare and Social Security - make up a huge chunk of the budget. They are fixed costs that can't easily be trimmed. Of the non-entitlement funds, fully one-half goes to defense. That leaves relatively little to tinker with.

Still, Bush is expected to hold increases in non-entitlement federal programs to about 4 percent. That compares with last year's increase of about 11 percent and the average annual increase in recent years of about 6 percent. Meanwhile, he has pledged to spend $50 billion over 10 years on education. He's also planning to boost spending for the National Institutes of Health by $2.8 billion next year. And he wants to add $5.7 billion for military housing, healthcare, and pay.

In general, Bush has public opinion behind him. "Americans still do not believe that the era of big government is over," despite President Clinton's declaration to that effect in 1995, says Karlyn Bowman, a public-opinion scholar at the American Enterprise Institute here. "They still think government should be put on a diet," she says, although, "They don't want to starve it."

The fact that Republicans now control both the White House and Congress also adds pressure on Bush to slow the rate of growth. "Over the past three years, no one was to blame [for big budget increases] because both sides were responsible," says budget guru Robert Reischauer, president of the Urban Institute here. But now, Republicans "can't exactly say, 'The Democrats made us do it' " if spending spirals up.

The risk, however, is that Bush could spark the kind of public backlash then-House Speaker Gingrich faced in 1995 when he tried to cut federal funding for school lunches. "These can't be Draconian cuts," says pollster Del Ali. "That's just not going to sell."

So, Bush has targeted some less-widely popular areas of the government, including the National Science Foundation. But he's also showing a willingness to tangle with his traditional allies. He apparently tried to trim the Energy Department's nuclear-stockpile program - although congressional conservatives appear to have prevailed in that fight, even winning a modest increase. And his plans to cut the Export-Import Bank's budget by some 24 percent have raised the ire of business interests.

"It's really good politics for Republicans to go after subsidies for Fortune 500 companies," says Mr. Moore of the Club for Growth. That balances any decreases that are especially unpopular with Democrats.

After his budget speech to Congress on Tuesday, Bush will release his full budget outline Wednesday. That's when the wrangling begins in earnest.